The below program is to check whether a number (say "n") prime factors are limited to 2,3,and 5 only or not. But program gives me signed integer overflow runtime error. Can anyone please help me in solving this problem? Here's the piece of code:

 bool check(int n)
   {
       if(n<0)
       n=n*(-1); // If 'n' is negative, making it positive.
       int count=1; //'count' variable to check whether the number is divisible by 2 or 3 or 5.
       while(n!=1 && count)
       {
           count=0;
           if(n%2==0)
           {
               n/=2; count  ;
           }
           else if(n%3==0)
           {
               n/=3; count  ;
           }
           else if(n%5==0)
           {
               n/=5; count  ;
           }
       }
       if(n==1)
       return true;
       else return false;
       
    }

Program gave me this error:

runtime error: signed integer overflow: -2147483648 * -1 cannot be represented in type 'int'

CodePudding user response：

-2147483648 * -1 cannot be represented in type 'int' [signed 32 bit]

For sure, it cannot, and you know why? A simple fact of representation.

Imagine to have 4 bits instead of 32. You would have 1 bit for the sign and 3 for the absolute value, right?

Well, lets say you have 0 for positive numbers and 1 for negative numbers in the first bit.

Then you can only represent 2^3=8 combinations for the absolute value, right? Well, you only have 8 positive numbers and 8 negative numbers.

BUT 0 is considered as positive, so you have 8 negative, 7 positive and 1 neutral. So you have numbers from -8 to 7.

In this case you have numbers from -2147483648 to 2147483647.

CodePudding user response：

If your prime factors are limited to be 2, 3, or 5, then the easiest way is:

if (n < 0) return false;

But if your prime factors can also be -1, then just make that as an acceptable valid terminal condition.

bool check(int n) {
    for (;;) {
        if (n%2 == 0) {
            n /= 2;
        } else if (n%3 == 0) {
            n /= 3;
        } else if (n%5 == 0) {
            n /= 5;
        } else {
            break;
        }   
    }   

    return (n == 1) || (n == -1);
}